Marine Biok Notes

Marine Biok Notes

Introduction to Light in Marine Systems

  • Marine Biok BR22620

  • Focus on the importance of light in oceanic ecosystems.

The Light Budget in Oceanic Systems

  • Ocean Surface and Atmosphere

    • Incoming solar radiation accounts for 100% of total energy.

    • Distribution of solar radiation:

    • 51% Absorbed by the ocean.

    • 20% Reflected by the ocean.

    • 16% Reflected by clouds.

    • 6% Reflected by the atmosphere.

    • Water absorption is affected by components such as H2O, O3, and dust.

  • Pattern of Absorption and Reflection:

    • 6% of incoming solar radiation is reflected by the air.

Angle of Incidence and Light Behavior

  • Angle of Incidence:

    • The greater the angle of incidence, the greater the reflectance of light.

  • Behavior of light upon entering water:

    • Scattering and absorption occurs.

    • Components causing scattering: Bacteria, plankton, and sediment.

    • Light absorption by marine plants leads to varied penetration depths:

    • At 1 cm depth, 73% light is absorbed.

    • At 10 m depth, 22.2% light is absorbed.

    • At 200 m depth, only 0.0062% remains.

Variation of Light with Depth

  • Spectral Quality and Quantity:

    • Changes significantly with depth in the water column.

    • Water absorbs red wavelengths readily; only 1% of red light remains at 10 m.

    • Blue wavelengths penetrate deeper, crucial for photosynthesis.

  • Light Intensity Decline:

    • Overall light intensity decreases exponentially with increasing depth.

Light Absorption Factors

  • Components Affecting Light Absorption:

    • Phytoplankton presence, dissolved substances, and suspended particles play a significant role in how light is absorbed in aquatic environments.

  • Temporal Variability in Light Absorption:

    • There are significant changes in light absorption over time.

Photosynthesis and Primary Productivity

  • Role of Light in Photosynthesis:

    • Light is the driving force behind photosynthesis and thus primary productivity in marine environments.

  • P/E Curve:

    • Illustrates the relationship between the rate of photosynthesis and irradiance (light intensity).

  • Critical Depth (Dc):

    • Defined as the depth where carbon fixed through photosynthesis equals that lost through respiration.

    • Can be illustrated in the context of phytoplankton mixing above and below this depth.

  • Compensation Depth (Dcr):

    • At this depth, the photosynthetic activity equals the respiration rate at a specific light level.

Productivity Dynamics

  • Low Phytoplankton Potential:

    • When Critical depth < Dcr, there is insufficient biomass for considerable productivity.

  • High Phytoplankton Potential:

    • When Critical depth > Dcr, phytoplankton can thrive and contribute to primary productivity.

  • Seasonal Variation:

    • Influenced by conditions of winter and spring.

Thermocline and Nutrient Dynamics

  • Influence of Thermocline on Primary Productivity:

    • In the Tropics: Local conditions lead to a permanent thermocline.

    • In Temperate Zones: The thermocline is disrupted by seasonal light and nutrient changes.

    • In the Poles: Limited light availability and absence of a thermocline.

  • Thermocline’s Role in Nutrient Availability:

    • Acts as a barrier affecting nutrient access and influences primary productivity.

Depth Zones and Light Availability

  • Mesopelagic Zone (200-1000 m):

    • Light is present but insufficient for photosynthesis.

  • Bathypelagic Zone (below 1000 m):

    • No light penetrates except bioluminescence from deep-sea organisms, primarily produced bacterially.

Additional Influencing Factors

  • Factors Influencing Light Dynamics:

    • Diel variations (day/night cycles), seasonal changes, latitude effects, particle density and size, as well as environmental factors such as upwelling, tides, currents, and land runoff.